JP5626602B2 - Nonaqueous electrolyte secondary battery - Google Patents

Description

  The present invention relates to a non-aqueous electrolyte secondary battery. Specifically, the present invention relates to a lithium secondary battery and other non-aqueous electrolyte secondary batteries that can be applied to a vehicle-mounted power source.

  Non-aqueous electrolyte secondary batteries such as lithium secondary batteries are preferably used as so-called portable power sources such as personal computers and portable terminals and vehicle power sources. In particular, a lithium ion secondary battery that is lightweight and has a high energy density is increasingly important as a high-output power source for driving vehicles such as electric vehicles and hybrid vehicles. Among such nonaqueous electrolyte secondary batteries, those using a positive electrode active material having a predetermined hollow structure can exhibit a high output at a low SOC (state of charge), so that an output at a low SOC is achieved. It is suitable for required applications (for example, as a power source for vehicles such as hybrid cars, plug-in hybrid cars, and electric cars).

  Also, this type of secondary battery is typically constructed by housing an electrode body in which a positive electrode and a negative electrode are stacked via a separator together with a nonaqueous electrolyte. The separator has a role of electrically insulating the positive electrode and the negative electrode and a role of holding a non-aqueous electrolyte. Further, the separator softens when the battery generates heat and reaches a certain temperature range (typically, the softening point or melting point of the material constituting the separator), and shuts down the conduction path of the charge carrier. It also has a function. Some of such separators are provided with a heat-resistant layer containing a filler such as alumina for the purpose of suppressing a short circuit due to thermal contraction of the separator. In general, when a battery generates heat due to a short circuit inside the battery, the vicinity of the short circuit point on the surface of the negative electrode becomes higher than other parts. Therefore, the above heat-resistant layer is disposed so as to face the negative electrode. Patent document 1 is mentioned as a literature concerning the prior art which disclosed this kind of heat-resistant layer.

JP2011-253684A

  The present inventors have examined thermal stability in a secondary battery using a positive electrode active material having a hollow structure, and have found a phenomenon peculiar to the positive electrode active material having a hollow structure. That is, when the battery generates heat due to overcharge or the like and the temperature inside the battery reaches a predetermined temperature or more, the separator softens and melts, but a part of the melted separator (hereinafter also referred to as melt). Can penetrate into the positive electrode. It has been found that the degree of penetration is larger than expected in the case of a positive electrode including a positive electrode active material having a hollow structure. Due to this phenomenon, when a positive electrode active material having a hollow structure is used, the shape of the separator (including the thickness and density of the separator) is reduced and the deformation of the separator (typically In particular, a film breakage is likely to occur. It has been found that this can contribute to an increase in leakage current in a secondary battery using a positive electrode active material having a hollow structure. And based on these discoveries, it came to complete this invention.

  That is, the present invention relates to an improvement in a non-aqueous electrolyte secondary battery using the hollow cathode active material, and an object thereof is to provide a non-aqueous electrolyte secondary battery with improved thermal stability. is there.

  In order to achieve the above object, the present invention provides a nonaqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode. The positive electrode of the secondary battery includes a positive electrode active material having a hollow structure having a shell portion and a hollow portion formed therein. In addition, a heat resistant barrier layer is disposed between the positive electrode and the separator.

  According to such a configuration, since the heat-resistant barrier layer is disposed between the positive electrode and the separator, the separator melt is blocked by the heat-resistant barrier layer and does not enter the positive electrode. Thereby, the fall of the shape retainability of a separator is suppressed, and as a result of the leakage current resulting from the fall of this shape retainability becoming small, thermal stability improves. As is clear from this explanation, the decrease in the shape retention of the separator is a phenomenon peculiar to a positive electrode using a positive electrode active material having a hollow structure, which is essentially different from the conventionally known thermal contraction of a separator. . Further, the suppression of the decrease in the shape retention of the separator by the heat-resistant barrier layer is different from the conventionally known thermal contraction suppression of the separator.

  In a preferred embodiment of the nonaqueous electrolyte secondary battery disclosed herein, the positive electrode active material has a particle porosity of 15% or more. It has now been clarified that the separator melt penetrates into the pores of the positive electrode active material, and the amount of penetration is such that the shape retention of the separator can be reduced. Therefore, the action by the heat-resistant barrier layer (that is, the action of blocking the separator from being melted by the rise of the battery temperature and partially entering the positive electrode) is effectively exerted against the above configuration. The thermal stability is remarkably improved.

  In a preferred embodiment of the nonaqueous electrolyte secondary battery disclosed herein, the thickness of the shell portion of the positive electrode active material is 2 μm or less. Since the positive electrode active material having such a structure tends to have a large volume (that is, particle porosity) in the hollow region of the particles, the effect of the heat-resistant barrier layer is effectively exhibited, and the thermal stability is remarkably improved. To do.

  In a preferred embodiment of the nonaqueous electrolyte secondary battery disclosed herein, the heat-resistant barrier layer has a thickness of 2 μm or more. The heat-resistant barrier layer having such a thickness can sufficiently block the separator melt from entering the positive electrode.

  In a preferred aspect of the nonaqueous electrolyte secondary battery disclosed herein, the separator is made of a polyolefin resin. The heat-resistant barrier layer contains a filler as a main component, and the filler is preferably at least one selected from the group consisting of alumina, boehmite, silica, titania, zirconia, calcia, and magnesia.

  Since the nonaqueous electrolyte secondary battery disclosed herein uses the positive electrode active material having the hollow structure, it can exhibit good output characteristics even in a low SOC range. Moreover, since the heat resistant barrier layer is disposed between the positive electrode and the separator, the thermal stability is also excellent. Therefore, taking advantage of this feature, it can be suitably used as a drive power source for vehicles such as hybrid vehicles (HV), plug-in hybrid vehicles (PHV), and electric vehicles (EV). According to the present invention, there is provided a vehicle equipped with any of the nonaqueous electrolyte secondary batteries disclosed herein (which may be in the form of an assembled battery in which a plurality of batteries are connected).

It is a perspective view which shows typically the external shape of the lithium secondary battery which concerns on one Embodiment. It is sectional drawing in the II-II line of FIG. It is a perspective view which shows typically the state which winds and produces the electrode body which concerns on one Embodiment. It is a figure which expands and shows a part of cross section of the structural example between the positive / negative electrodes of FIG. It is sectional drawing which shows typically the positive electrode active material which has the hollow structure which concerns on one Embodiment. It is a figure explaining the relationship between the electric current of a lithium secondary battery at the time of overcharge, and the temperature in a battery. It is a side view showing typically a vehicle (automobile) provided with a lithium secondary battery concerning one embodiment.

  Embodiments according to the present invention will be described below with reference to the drawings. Note that the dimensional relationship (length, width, thickness, etc.) in each drawing does not reflect the actual dimensional relationship. Further, matters other than matters specifically mentioned in the present specification and matters necessary for the implementation of the present invention (for example, a configuration and a manufacturing method of an electrode body including a positive electrode and a negative electrode, a configuration and a manufacturing method of a separator and an electrolytic solution) The general shape and the like related to the construction of the battery, such as the shape of the battery (case), can be understood as the design items of those skilled in the art based on the prior art in this field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field. Further, in the following drawings, members / parts having the same action are described with the same reference numerals, and overlapping descriptions may be omitted or simplified.

  As a preferred embodiment of the nonaqueous electrolyte secondary battery disclosed herein, a lithium secondary battery will be described as an example. However, the application target of the present invention is not intended to be limited to such a battery. For example, the present invention can also be applied to a non-aqueous electrolyte secondary battery that uses a metal ion (for example, sodium ion) other than lithium ion (Li ion) as a charge carrier. In the present specification, “secondary battery” generally refers to a battery that can be repeatedly charged and discharged. In addition to a storage battery (ie, a chemical battery) such as a lithium secondary battery, a capacitor (ie, a physical battery) such as an electric double layer capacitor. ). Further, in this specification, the “lithium secondary battery” refers to a secondary battery that uses Li ions as electrolyte ions and is charged / discharged by the movement of charges accompanying Li ions between the positive and negative electrodes. A battery generally called a lithium ion secondary battery is a typical example included in the lithium secondary battery in this specification.

≪Lithium secondary battery≫
As shown in FIGS. 1 and 2, the lithium secondary battery 100 includes a box-shaped rectangular battery case 10 and a wound electrode body 20 accommodated in the battery case 10. The battery case 10 has an opening 12 on the upper surface. The opening 12 is sealed by the lid 14 after the wound electrode body 20 is accommodated in the battery case 10 from the opening 12. The battery case 10 also contains a nonaqueous electrolyte (nonaqueous electrolyte solution) 25. The lid body 14 is provided with an external positive terminal 38 and an external negative terminal 48 for external connection, and a part of the terminals 38 and 48 protrudes to the surface side of the lid body 14. A part of the external positive terminal 38 is connected to the internal positive terminal 37 inside the battery case 10, and a part of the external negative terminal 48 is connected to the internal negative terminal 47 inside the battery case 10.

  As shown in FIG. 3, the wound electrode body 20 includes a long sheet-like positive electrode (positive electrode sheet) 30 and a long sheet-like negative electrode (negative electrode sheet) 40. The positive electrode sheet 30 includes a long positive electrode current collector 32 and a positive electrode mixture layer 34 formed on at least one surface (typically both surfaces) thereof. The negative electrode sheet 40 includes a long negative electrode current collector 42 and a negative electrode mixture layer 44 formed on at least one surface (typically both surfaces) thereof. The wound electrode body 20 also includes two long sheet-like separators (separator sheets) 50A and 50B. The positive electrode sheet 30 and the negative electrode sheet 40 are laminated via two separator sheets 50A and 50B, and the positive electrode sheet 30, the separator sheet 50A, the negative electrode sheet 40, and the separator sheet 50B are laminated in this order. The laminated body is formed into a wound body by being wound in the longitudinal direction, and is further formed into a flat shape by crushing the rolled body from the side surface direction and causing it to be ablated. The electrode body is not limited to a wound electrode body. An appropriate shape and configuration can be appropriately employed depending on the shape of the battery and the purpose of use.

  The positive electrode mixture layer 34 formed on the surface of the positive electrode current collector 32 and the negative electrode formed on the surface of the negative electrode current collector 42 are disposed at the center in the width direction perpendicular to the winding direction of the wound electrode body 20. A portion in which the composite material layer 44 overlaps and is densely stacked is formed. Further, at one end in the width direction of the positive electrode sheet 30, a portion where the positive electrode current collector layer 34 is not formed and the positive electrode current collector 32 is exposed (positive electrode mixture layer non-forming portion 36) is provided. . The positive electrode mixture layer non-forming portion 36 is in a state of protruding from the separator sheets 50 </ b> A and 50 </ b> B and the negative electrode sheet 40. That is, the positive electrode current collector laminated portion 35 in which the positive electrode mixture layer non-forming portion 36 of the positive electrode current collector 32 overlaps is formed at one end in the width direction of the wound electrode body 20. Further, similarly to the case of the positive electrode sheet 30 at one end, the negative electrode current collector stack in which the negative electrode mixture layer non-forming portion 46 of the negative electrode current collector 42 is overlapped with the other end in the width direction of the wound electrode body 20. A portion 45 is formed. The separator sheets 50 </ b> A and 50 </ b> B have a width that is larger than the width of the laminated portion of the positive electrode mixture layer 34 and the negative electrode mixture layer 44 and smaller than the width of the wound electrode body 20. By arranging this so as to be sandwiched between the laminated portions of the positive electrode mixture layer 34 and the negative electrode mixture layer 44, the positive electrode mixture layer 34 and the negative electrode mixture layer 44 are prevented from coming into contact with each other to cause an internal short circuit. .

  The separator sheet 50A is composed of a porous resin layer, and as shown in FIG. 4, a heat-resistant blocking layer 51 is formed on the surface of the separator sheet 50A on the positive electrode sheet 30 side. The heat-resistant blocking layer 51 is formed over the entire surface of the separator sheet 50A, that is, over the entire length direction (winding direction) and width direction of the separator sheet 50A. FIG. 4 schematically shows that the positive electrode mixture layer 34 includes the positive electrode active material 110 having a hollow structure.

  With the above configuration, a decrease in the shape retaining property of the separator sheet 50A is suppressed, and a leakage current resulting from the decrease in the shape retaining property is reduced. As a result, the thermal stability is improved. This mechanism will be described. When the battery generates heat due to overcharging or the like and reaches a predetermined temperature or higher, the separator sheet 50A melts. At this time, if the positive electrode sheet 30 (typically, the positive electrode mixture layer 34) including the positive electrode active material 110 having a hollow structure and the separator sheet 50A are opposed (typically adjacent), the separator sheet 50A described above. It was revealed that the molten material entered the positive electrode mixture layer 34 and diffused to the inside (hollow part) of the particles of the positive electrode active material 110 having a hollow structure. Therefore, the degree of penetration of the melt into the positive electrode mixture layer 34 including the positive electrode active material layer 110 including the hollow structure positive electrode active material 110 is larger than that of the positive electrode mixture layer including the solid structure positive electrode active material, The shape retainability of the separator sheet 50A decreases. Typically, the thickness of the separator sheet 50A is reduced, and a low density portion is generated. Such a decrease in shape retainability is considered to cause a deformation (typically a membrane breakage) of the separator sheet 50A, which tends to increase the leakage current. However, according to the above configuration, since the heat-resistant blocking layer 51 is disposed between the positive electrode sheet 30 and the separator sheet 50A, the melt of the separator sheet 50A is blocked by the heat-resistant blocking layer 51, and the positive electrode Does not penetrate. Thereby, the fall of the shape retainability of a separator is suppressed, and as a result of the leakage current resulting from the fall of this shape retainability becoming small, thermal stability improves. The above configuration may be a configuration in which the separator and the negative electrode face each other, but it has been confirmed that the separator melted due to the heat generated by the battery does not enter the negative electrode (typically, the negative electrode mixture layer). Yes.

  Note that the heat-resistant barrier layer only needs to be disposed between the positive electrode and the separator, and is not limited to those formed on the separator. For example, a heat resistant barrier layer may be formed on at least one surface of the positive electrode. Moreover, you may form a heat-resistant interruption | blocking layer on both surfaces of a separator. Furthermore, a heat-resistant layer other than the heat-resistant barrier layer (a layer having a composition different from that of the heat-resistant barrier layer) may be disposed between the positive and negative electrodes. The separator is not limited to a single-layer structure, and may have a multilayer structure of two or more layers. A typical example is a three-layer film made of polypropylene / polyethylene / polypropylene. Since the configuration of separator sheet 50B is basically the same as that of separator sheet 50A, description thereof will not be repeated. In addition, when using, for example, a solid (gel) electrolyte in which a polymer is added to the electrolytic solution instead of the electrolytic solution, the electrolyte itself can function as a separator, and thus a separator may be unnecessary. obtain.

≪Positive electrode≫
There is no restriction | limiting in particular in the component which comprises a lithium secondary battery other nonaqueous electrolyte secondary battery, About the matter other than mentioning later, the structure similar to the component of the conventional secondary battery is employable. For example, a conductive member made of a highly conductive metal is preferably used for the positive electrode current collector. As such a conductive member, for example, aluminum or an alloy containing aluminum as a main component can be used. The shape of the positive electrode current collector can be different depending on the shape of the battery and is not particularly limited, and may be various forms such as a rod shape, a plate shape, a sheet shape, a foil shape, and a mesh shape. The thickness of the positive electrode current collector is not particularly limited, and can be about 5 to 30 μm.

<Positive electrode active material>
(Basic composition)
The positive electrode mixture layer contains a positive electrode active material. The positive electrode active material includes a lithium transition metal oxide having a layered crystal structure (typically a layered rock salt structure belonging to a hexagonal system). The lithium transition metal oxide containing a metal element M _T. The _{M T} is at least one of Ni, Co and Mn. The total content of Ni, Co and Mn in the positive electrode active material (i.e., the content of M _T) is 100 mol% the total amount of all metal elements M _all other than lithium contained in the positive electrode active material in mole percentage Then, for example, it may be 85 mol% or more (preferably 90 mol% or more, typically 95 mol% or more). The positive electrode active material having the composition described above M _T contains at least Ni is preferable. For example, a positive electrode active material containing Ni in an amount of 10 mol% or more (more preferably 20 mol% or more) is preferable, where the total amount of metal elements other than lithium contained in the positive electrode active material is 100 mol%. The positive electrode active material having such a composition is suitable for producing positive electrode active material particles having a hollow structure by applying a production method described later.

As a preferred example of the lithium transition metal oxide, the M _T is Ni, lithium transition metal oxide containing all of Co and Mn (sometimes to hereinafter referred to as "LNCM oxide".) And the like. For example, the atomic basis, Ni, the total amount of Co and Mn (i.e. the amount of _{M T (m MT))} as 1, Ni, 0.7 more than the amount of Co and Mn is more than 0 none (e.g. LNCM oxide that is more than 0.1 and less than or equal to 0.6, typically more than 0.3 and less than or equal to 0.5 can be preferably employed. The ternary lithium transition metal oxide (LNCM oxide) is of a composition containing excess Li against _{M T} (i.e., LNCM oxide satisfying _{1.00 <(m Li / m MT} )) Is preferable because it is easy to synthesize. This is presumably because the LNCM oxide has a property of easily taking an excessive amount of Li into the transition metal layer in the above-described laminated structure. Here _(m Li _{/ m MT)} is the ratio of the number of moles of _{M T (m MT)} number of moles of Li with respect to _{(m Li)} (molar ratio). In one preferred embodiment, the amount of M _T (atomic number basis) as 1, is in an amount that generally comparable amount and Mn of Ni (e.g., the difference between the amount and the amount of Mn and Ni is 0.1 or less) . For example, a composition in which the amounts of Ni, Co, and Mn are approximately the same can be preferably used. The LNCM oxide having the above composition is preferable because it exhibits excellent thermal stability as a positive electrode active material.

In addition to M _T (that is, at least one of Ni, Co, and Mn), the positive electrode active material in the technology disclosed herein includes one or more other elements as additional constituent elements (additive elements). It can contain elements. Examples of the additional element include Group 1 (alkali metals such as sodium), Group 2 (alkaline earth metals such as magnesium and calcium), Group 4 (transition metals such as titanium and zirconium), Group 6 ( Any of those belonging to group 8 (transition metals such as chromium and tungsten), group 8 (transition metals such as iron), group 13 (metals such as boron or a metalloid element) and group 17 (halogens such as fluorine) Can be included. Typical examples include W, Cr, Mo, Zr, Mg, Ca, Na, Fe, Zn, Si, Sn, Al, B, and F. The total content of these additional constituent element is suitable to be less than 20 mole% of M _T, preferably in the ratio of 10 mol% or less. Positive electrode active material according to the preferred embodiment comprises as the additional element, W, at least one metallic element M _A is selected from Cr and Mo. In particular, the positive electrode active material composition including at least W as M _A is preferred. By containing W, the effect of reducing the reaction resistance of the battery using the positive electrode active material can be exhibited. This can also contribute to improving the output of the battery.

Content _{m A} of _{M A} (e.g. W) in the cathode active material, the total mole number _{m MT} of _{M T} contained in the positive electrode active material as 100 mol% in mole percentage, for example, a 0.001 mole% In general, it is appropriate to adjust to 0.01 to 3 mol%, and 0.05 to 1 mol% (more preferably 0.1 to 1 mol%, for example 0.2 to 1 mol%). It is preferable that Further, the content of _{m A} of _{M A} (e.g. W) in the positive electrode active material, the total number of moles _{m Mall} of all metal elements _{M all} other than Li contained in the positive electrode active material as 100 mol% in mole percentage, 0 0.001 to 5 mol%, usually 0.01 to 3 mol% is appropriate, 0.05 to 1 mol% (more preferably 0.1 to 1 mol%, for example 0 .2 to 1 mol%). If m _A or _{m Mall} is too small, the growth and the effect of suppressing the major axis direction of the primary particle size of the positive electrode active material is calculated from the XRD analysis of the positive electrode active material (003) plane / (104) half width ratio of surface and The effect of optimizing the (104) plane / (003) area width ratio (SF value: Stacking Factor value) cannot be obtained, and the battery output tends not to be improved. If m _A or m _Mall is too large, compared to the positive active material containing no M _A, the reaction resistance of the battery using the positive electrode active material may increase rather.

In a preferred embodiment, the positive electrode active material may have a composition (average composition) represented by the following general formula (I).
Li _{1 + x} Ni _y Co _z Mn _(1-yz) M _Aα M _Bβ O ₂ (I)
In the above formula (I), x may be a real number that satisfies 0 ≦ x ≦ 0.2. y may be a real number that satisfies 0.1 <y <0.6. z may be a real number that satisfies 0.1 <z <0.6. M _A is at least one metal element selected from W, Cr, and Mo, and α is 0 <α ≦ 0.01 (typically 0.0005 ≦ α ≦ 0.01, for example, 0.001. ≦ α ≦ 0.01). M _B is, Zr, Mg, Ca, Na , Fe, Zn, Si, Sn, Al, is one or more elements selected from the group consisting of B and F, beta is 0 ≦ β ≦ 0 .01 can be a real number. β is substantially zero (i.e., substantially free oxide M _B) may be.
Note that in this specification, in the chemical formulas representing the lithium transition metal oxide having a layered structure, the composition ratio of O (oxygen) is shown as 2 for convenience, but this numerical value should not be strictly interpreted, Variation in the composition (typically included in the range of 1.95 to 2.05).

(Hollow structure)
The positive electrode active material in the technology disclosed herein typically has a hollow particle form having a shell and a hollow (cavity) formed therein. The particle shape of the particulate positive electrode active material (positive electrode active material particle) may typically be approximately spherical, slightly distorted spherical, or the like. In a preferred embodiment, the shell portion has a through hole that allows the hollow portion and the outside of the particle to communicate with each other. Hereinafter, the hollow structure having the through hole in the shell portion is sometimes referred to as “perforated hollow structure”. In addition, as a thing contrasted with the particle | grains of such a hollow structure (it is the meaning which includes a void | hole hollow structure unless it mentions specially), the particle | grains of a general porous structure are mentioned. Here, the porous structure refers to a structure (sponge-like structure) in which a substantial part and a void part are mixed over the entire particle. As a typical example of the positive electrode active material particles having a porous structure, positive electrode active material particles obtained by a so-called spray firing method (sometimes referred to as a spray dry production method) can be given. The positive electrode active material particles having a hollow structure disclosed here are such that the substantial part is biased toward the shell part, and a space is clearly formed in the hollow part, and the hollow part is collected. The positive electrode active material particle having the porous structure is that the space is larger than the gap existing between the primary particles constituting the secondary particles (between adjacent primary particles that are sintered and adjacent to each other). The structure is clearly distinguished.

  The positive electrode active material according to a preferred embodiment is in the form of secondary particles in which primary particles of the lithium transition metal oxide are collected. Here, the “primary particle” refers to a particle that is considered to be a unit particle (ultimate particle) based on an apparent geometric form. In the positive electrode active material disclosed herein, the primary particles are typically a collection of crystallites of a lithium transition metal oxide. The shape of the positive electrode active material can be observed with a SEM (Scanning Electron Microscope) image.

  A typical structure of the positive electrode active material particles described above is schematically shown in FIG. The positive electrode active material particle 110 is a hollow structure particle having a shell portion 115 and a hollow portion 116. The shell portion 115 has a form in which the primary particles 112 are gathered in a spherical shell shape. In a preferred embodiment, the shell 115 has a form in which the primary particles 112 are arranged in a ring shape (beaded) in the cross-sectional SEM image. The primary particles 112 may be in a single (single layer) continuous form over the entire shell 115, or two or more primary particles 112 may be stacked (in multiple layers) to have a continuous part. Good. The number of stacked primary particles 112 in the continuous portion is preferably about 5 or less (for example, 2 to 5), and more preferably about 3 or less (for example, 2 to 3). The positive electrode active material particles 110 according to a preferred embodiment are configured such that the primary particles 112 are substantially continuous in a single layer over the entire shell 115.

  The positive electrode active material particles (secondary particles) 110 having the above-described configuration have less aggregation of the primary particles 112 than the positive electrode active material particles having a dense structure without a cavity inside. For this reason, there are few grain boundaries in the particles (as a result, the diffusion distance of Li ions is shorter), and the diffusion of Li ions into the particles is fast. According to such positive electrode active material particles 110 with few grain boundaries, the output characteristics of the lithium secondary battery having the particles 110 can be effectively improved. For example, a lithium secondary battery that exhibits good output even in a low SOC region (for example, when the SOC is 30% or less) where ion diffusion into the positive electrode active material is rate-limiting can be constructed.

(Through hole)
The positive electrode active material particle 110 preferably has a through hole 118 that passes through the shell portion 115 and spatially continues the hollow portion 116 and the outside (outside of the particle 110). By having the through-hole 118, the electrolytic solution easily goes back and forth between the hollow portion 116 and the outside, and the electrolytic solution in the hollow portion 116 is appropriately replaced. For this reason, withering of the electrolyte is insufficient in the hollow portion 116, and the primary particles 112 facing the hollow portion 116 can be more actively used for charging and discharging. According to this configuration, the electrolytic solution can be efficiently contacted with the primary particles 112, so that the output characteristics (especially the output characteristics in the low SOC region) of the lithium secondary battery can be further improved.

  The number of through-holes 118 included in the positive electrode active material particles 110 is preferably about 1 to 10 (for example, 1 to 5) as an average per particle of the active material particles 110. If the average number of through holes is too large, it may be difficult to maintain the hollow shape. According to the positive electrode active material particles 110 having a preferable average number of through-holes disclosed herein, the battery performance improvement effect (for example, the output is improved) by having a holed hollow structure while ensuring the strength of the positive electrode active material particles 110. Effect) can be exhibited satisfactorily and stably.

The opening width h of the through hole 118 is preferably about 0.01 μm or more as an average value of the plurality of positive electrode active material particles. Here, the opening width h of the through hole 118 refers to a passing length in the narrowest part of the path from the outside of the positive electrode active material particle 110 to the hollow part 116. When the opening width of the through holes 118 is 0.01 μm or more on average, the through holes 118 can function more effectively as a flow path for the electrolytic solution. Thereby, the effect which improves the battery performance of a lithium secondary battery can be exhibited more appropriately.
When one positive electrode active material particle 110 has a plurality of through holes 118, the opening width of the through hole having the largest opening width among the plurality of through holes 118 is adopted as the opening width of the active material particles 110. Good. The opening width h of the through holes 118 may be an average of 2.0 μm or less, more preferably an average of 1.0 μm or less, and even more preferably an average of 0.5 μm or less.

  The characteristic values such as the average number of through holes and the average opening size can be grasped by, for example, observing the cross section of the positive electrode active material particles with an SEM. For example, a sample obtained by solidifying positive electrode active material particles or a material containing the active material particles with an appropriate resin (preferably a thermosetting resin) is cut in an appropriate cross section, and SEM observation is performed while cutting the cut surface little by little. It is good to do. Or, since the orientation (posture) of the positive electrode active material particles can be generally assumed to be almost random in the above sample, the SEM observation results on a single cross section or a relatively small number of cross sections of about 2 to 10 locations are statistical. The above characteristic value can also be calculated by processing the above.

  In a preferred embodiment, as schematically shown in FIG. 5, the shell portion 115 is dense in a portion other than the through-hole 118 (typically dense enough not to pass at least a general non-aqueous electrolyte). ) Sintered. According to the positive electrode active material particles 110 having this structure, the locations where the electrolytic solution can flow between the outside of the particles 110 and the hollow portions 116 are limited to the locations where the through holes 118 are provided. Thereby, for example, particularly advantageous effects can be exhibited in the positive electrode active material particles used for the positive electrode of a battery including a wound electrode body. That is, in a battery including a wound electrode body, when charging and discharging of the battery is repeated, the electrolyte is squeezed out from the electrode body (particularly, the positive electrode mixture layer) due to expansion and contraction of the positive electrode active material that accompanies charging and discharging. Battery performance (for example, output performance) may be deteriorated due to insufficient electrolyte in a part of the electrode body. According to the positive electrode active material particles 110 having the above-described configuration, the electrolyte solution in the hollow portion 116 is prevented from flowing out at portions other than the through-holes 118, so that the shortage of electrolyte solution (liquid withering) in the positive electrode mixture layer is effectively prevented. Can be prevented or reduced. Moreover, since the positive electrode active material particles 110 can have a high shape-maintaining property (being difficult to collapse; for example, it can be reflected in a high average hardness, a high compressive strength, etc.), good battery performance is more stable. Can be demonstrated.

(Particle porosity)
The positive electrode active material in the technology disclosed herein has a hollow structure (typically a holed hollow structure) having a particle porosity of 5% or more. A positive electrode active material having a particle porosity of 10% or more is preferable, and more preferably 15% or more. If the particle porosity is too small, the advantage of having a hollow structure may not be sufficiently exerted. The particle porosity may be 20% or more (typically 23% or more, preferably 30% or more). The upper limit of the particle porosity is not particularly limited, but the durability of the positive electrode active material particles (for example, the ability to withstand compressive stress that can be applied during battery production or use and maintain a hollow shape), ease of production, etc. In view of this, it is usually appropriate to use 95% or less (typically 90% or less, for example 80% or less). The adjustment of the particle porosity is performed, for example, in the method for producing a positive electrode active material to be described later, through the time during which the particle growth process is continued, the precipitation rate of transition metal hydroxide (for example, ammonia concentration) in the particle growth process, and the like. be able to.

Here, the “particle porosity” refers to the ratio of the hollow portion in the apparent cross-sectional area of the active material in the average of the cross sections obtained by cutting the positive electrode active material at random positions. This ratio can be grasped, for example, through an SEM image in an appropriate cross section of the positive electrode active material particles or the material containing the active material particles. The cross-sectional SEM image is obtained, for example, by cutting a sample obtained by solidifying positive electrode active material particles or a material containing the active material particles with an appropriate resin (preferably a thermosetting resin), and observing the cross-section by SEM. be able to. In the cross-sectional SEM image, the shell part, the hollow part, and the through hole of the positive electrode active material particle can be distinguished by the difference in color tone or light and shade. For a plurality of positive electrode active material particles displayed in an arbitrary cross-sectional SEM image of the sample, the area _CV occupied by the hollow portion of the positive electrode active material particles, and the cross-sectional area apparently occupied by the positive electrode active material particles obtaining a ratio of _{C T (C V / C T} ). Here, the cross-sectional area C _T occupied on the positive electrode active material particles apparently refers shell of the positive electrode active material particle, the cross-sectional area occupied by the hollow portion and the through-hole. By the ratio (C _V / C _T ), the ratio of the hollow portion to the apparent volume of the positive electrode active material particles (that is, the particle porosity) is generally determined.

Preferably, the value of the ratio (C _V / C _T ) is arithmetically averaged for an arbitrary plurality of cross-sectional SEM images of the sample. In this way, the ratio _(C V _/ C _T) as the number of cross-sectional SEM image increases seeking, also the ratio _(C V _/ C _T) as the number of the positive electrode active material particles is often the basis for calculating the above ratios The arithmetic average value of (C _V / C _T ) converges. Usually, it is preferable to determine the particle porosity based on at least 10 (for example, 20 or more) positive electrode active material particles. Moreover, it is preferable to obtain | require particle | grain porosity based on the SEM image in the cross section of the arbitrary 3 places (for example, 5 places or more) of a sample at least.

(Thickness of shell)
In the positive electrode active material having a hollow structure (positive electrode active material particles), the thickness of the shell portion (portion where primary particles are gathered in a spherical shell shape) is preferably 3.0 μm or less, more preferably 2.5 μm or less ( For example, it is 2.2 μm or less), more preferably 2.0 μm or less (for example, 1.5 μm or less). The smaller the thickness of the shell portion, the easier it is to release Li ions from the inside of the shell portion (the central portion of the thickness) during charging, and the more easily the Li ions are absorbed to the inside of the shell portion during discharging. Accordingly, the amount of Li ions that can be occluded and released by the unit mass of the positive electrode active material particles under a predetermined condition can be increased, and the resistance when the positive electrode active material particles occlude and release Li ions can be reduced. . A lithium secondary battery using the above positive electrode active material particles can be excellent in output in a low SOC region. In other words, the Li solid diffusion property of the positive electrode active material is rate-determining for the output in the low SOC region, and the Li diffusion distance affects the Li solid diffusion property. Therefore, the positive electrode active material that affects this Li diffusion distance. Since the shell thickness of the particles is small, the output characteristics in the low SOC region can be excellent.

  Although the lower limit of the thickness of the shell is not particularly limited, it is generally preferable that the thickness is approximately 0.1 μm or more. Maintaining higher durability against stress that can be applied during battery manufacture or use, and expansion and contraction of the positive electrode active material associated with charge and discharge, by making the thickness of the shell portion 0.1 μm or more Can do. Thereby, the performance of the lithium secondary battery can be stabilized. From the viewpoint of achieving both an internal resistance reduction effect and durability, the thickness of the shell is preferably about 0.1 μm to 2.2 μm, more preferably 0.2 μm to 2.0 μm, and 0 It is particularly preferable that the thickness is 5 μm to 1.5 μm.

  Here, the thickness of the shell portion 115 (see FIG. 5) refers to the inner side surface 115a of the shell portion 115 (however, the portion corresponding to the through hole 118) in the cross-sectional SEM image of the positive electrode active material or the material containing the active material particles. Is not included in the inner side surface 115a.) The average value of the shortest distance T (k) from any position k to the outer side surface 115b of the shell 115. More specifically, the shortest distance T (k) may be obtained for a plurality of positions on the inner surface 115a of the shell 115, and the arithmetic average value thereof may be calculated. In this case, as the number of points for obtaining the shortest distance T (k) is increased, the thickness T of the shell portion 115 converges to an average value, and the thickness of the shell portion 115 can be appropriately evaluated. Usually, it is preferable to determine the thickness of the shell 115 based on at least 10 (for example, 20 or more) positive electrode active material particles 110. In addition, it is preferable to obtain the thickness of the shell 115 based on SEM images at least at three (eg, five or more) cross sections of the sample (eg, any one of the positive electrode active materials).

(Secondary particles)
The average particle size (secondary particle size) of the positive electrode active material particles is preferably about 2 μm to 25 μm, for example. According to the positive electrode active material having such a configuration, good battery performance can be more stably exhibited. If the average particle size is too small, the volume of the hollow portion is small, and the effect of improving battery performance may tend to decrease. The average particle size is more preferably about 3 μm or more. From the viewpoint of the productivity of the positive electrode active material and the productivity of the positive electrode mixture layer that is a thin film peculiar to HV, the average particle size is preferably about 25 μm or less, and about 15 μm or less (for example, about 10 μm or less). ) Is more preferable. In a preferred embodiment, the average particle diameter of the positive electrode active material is about 3 μm to 10 μm (for example, 3 μm to 8 μm).

The average particle diameter of the positive electrode active material particles can be determined as a volume-based median diameter (D ₅₀ : 50% volume average particle diameter) measured by a method known in the art, for example, a laser diffraction scattering method. In addition, for example, in the method for producing a positive electrode active material described later, the average particle size is adjusted by adjusting the pH at the nucleation stage, the time for continuing the particle growth process, and the deposition rate of the transition metal hydroxide at the particle growth process. Etc. can be performed. The deposition rate of the transition metal hydroxide is adjusted through, for example, the concentration, pH, reaction system temperature, etc. of one or more chemical species related to Formula 1 or Formula 2 in the method for producing a positive electrode active material described below. Can do. Alternatively, the average particle diameter may be adjusted by selecting particles by general sieving. Such an average particle diameter adjusting method can be carried out alone or in appropriate combination.

(Primary particles)
Referring to FIG. 5, primary particles 112 constituting positive electrode active material particles 110 may have a major axis L1 of, for example, approximately 0.1 μm to 1.0 μm. According to the knowledge of the present inventors, the major axis L1 of the primary particle 112 can be generally correlated with the crystal size in the direction orthogonal to the normal direction (c-axis) of the (003) plane. If L1 is too small, the capacity maintenance of the battery may tend to decrease. From such a viewpoint, L1 is preferably 0.2 μm or more, more preferably 0.3 μm or more, and further preferably 0.4 μm or more. On the other hand, if L1 is too large, the distance (Li ion diffusion distance) from the surface of the crystal to the inside (the center portion of L1) becomes long, so that the ion diffusion into the crystal becomes slow, and the output characteristics (particularly low The output characteristics in the SOC region tend to be low. From such a viewpoint, L1 is preferably 0.8 μm or less (for example, 0.75 μm or less). In a preferred embodiment, the major particle L1 of the primary particles is 0.2 μm to 0.8 μm (for example, 0.3 μm to 0.75 μm).

The major axis L1 of the primary particle 112 can be measured based on, for example, an SEM image of the particle surface of the positive electrode active material particle (secondary particle) 110. When measuring the long diameter L1 of the primary particles (particle diameter P _{1 of the} primary particles) of the positive electrode active material particles contained in the positive electrode mixture layer of the lithium secondary battery, it appears in a cross section obtained by dividing the mixture layer. SEM observation of the surface of the positive electrode active material particles may be performed. For example, in the SEM image, primary particles 112 suitable for specifying the major axis L1 are specified. That is, since a plurality of primary particles 112 are shown in the SEM image of the particle surface of the positive electrode active material particles (secondary particles) 110, a plurality of these primary particles 112 are extracted in descending order of the display area in the SEM image. To do. Thereby, in the SEM image of the particle surface, it is possible to extract the primary particles 112 in which the outer shape along the longest major axis L1 is reflected. And it is good to make the length of the longest long axis in the extracted primary particle 112 into the major axis L1. In this specification, major axis L1 can also mean particle diameter P ₁ of the primary particles of the positive electrode active material.

(crystalline)
In the positive electrode active material disclosed here, the transition metal layer is laminated in any manner. In other words, transition metal layers are randomly stacked when no interaction acts in the stacking direction, but can have a layer structure with regularity in the stacking mode when interactions appear in the stacking direction. It is guessed. At this time, the irregularity in the stacking direction and the degree of regularity are the diffraction peak of the (003) plane located at a diffraction angle 2θ = 17 to 20 ° when X-ray diffraction measurement is performed using a Cu tube. It is considered possible to draw by comparing the diffraction peak shapes of the (104) plane located at 2θ = 43 to 46 °. That is, when the shape of the diffraction peak of the (104) plane relative to the shape of the diffraction peak of the (003) plane is quantified using the SF value, that is, the ratio of (104) plane / (003) area width is quantified. In this case, when the regularity in the stacking direction is high, the SF value tends to increase, and when the SF value satisfies 1.0 ≦ SF ≦ 2.6, the regularity in the stacking direction is considered to be more optimal. Can be. In the case of a sample having a high regularity in the SF value and stacking direction and a large interaction, the diffusion of Li ions in the solid is accelerated, the output characteristics in the low SOC region are improved, and the layer structure is formed even in an oxidized state in which Li ions are extracted. Since it is stabilized, it is considered that the positive electrode material is excellent in charge / discharge durability. When the SF value is lower than 1.0, the interaction in the stacking direction is insufficient, and when the SF value is higher than 2.6, the interaction in the stacking direction becomes too strong, and Li ion transport in the solid is inhibited. It is thought that it will be done. The SF value is more preferably 1.3 or more, further preferably 1.5 or more, and the SF value is further preferably 2.4 or less (for example, 2.2 or less).

The method for measuring the crystalline SF value is not particularly limited, but can be performed by powder X-ray diffraction measurement of a sample. The measurement can be performed using an X-ray diffractometer (RINT2200 manufactured by Rigaku Corporation) using CuKα rays (wavelength 0.154051 nm) as radiation. X-ray monochromation can be performed by using a graphite single crystal monochromator and setting the applied voltage to 40 kV and a current of 30 mA. Further, it is desirable that the measurement is performed at a scanning speed of 3 ° / min and in an angle range of 2θ = 10 ° to 100 °. Integral intensity ratio R _I between diffraction peak A located at diffraction angle 2θ = 17 to 20 ° and diffraction peak B located at 2θ = 43 to 46 ° when X-ray diffraction measurement is performed using a Cu tube. The SF value (= R _H / R _I ) can be calculated from (= I _A / I _B ) and the peak intensity ratio R _H (= H _A / H _B ).

(Specific surface area)
The BET specific surface area of the positive electrode active material disclosed herein is preferably about 0.3 m ² / g or more, more preferably 0.5 m ² / g or more, and 0.8 m ² / g or more. More preferably it is. Further, the BET specific surface area of the positive electrode active material particles 110 can be, for example, approximately 3.0 m ² / g or less (for example, 2.0 m ² / g or less), and can be 1.7 m ² / g or less. It may be 1.5 m ² / g or less. The positive electrode active material according to a preferred embodiment has a BET specific surface area of approximately 0.5 to 2.0 m ² / g.

(Positive electrode active material hardness)
According to a preferred embodiment of the technology disclosed herein, positive electrode active material particles having an average hardness of approximately 0.5 MPa or more (typically 1.0 MPa or more, for example, 2.0 to 10 MPa) can be produced. Here, the “average hardness” refers to a value obtained by dynamic microhardness measurement performed using a flat diamond indenter with a diameter of 50 μm and under a load speed of 0.5 mN / sec to 3 mN / sec. For the dynamic microhardness measurement, for example, a microhardness meter manufactured by Shimadzu Corporation, model “MCT-W500” can be used. The more the positive electrode active material particles are subjected to the above hardness measurement, the more the arithmetic average value of the hardness of those positive electrode active materials converges. As the average hardness, it is preferable to employ an arithmetic average value based on at least three (preferably five or more) positive electrode active material particles. A method for producing a positive electrode active material described later including a nucleation step and a particle growth step is suitable as a method for producing a positive electrode active material having the above average hardness. The positive electrode active material particles having a perforated hollow structure obtained by this method are compared with the positive electrode active material particles having a general porous structure obtained by, for example, a spray firing method (also referred to as a spray dry method). It can be harder (higher average hardness) and excellent in form stability. As described above, the positive electrode active material particles having a hollow structure and high average hardness (in other words, high shape maintaining property) can provide a battery that stably exhibits higher performance.

<Method for producing positive electrode active material>
The manufacturing method of a positive electrode active material includes a raw material hydroxide production | generation process, a mixing process, and a baking process, for example. The raw material hydroxide generation step is a step of supplying ammonium ions to the aqueous solution of the transition metal compound to precipitate the transition metal hydroxide particles from the aqueous solution. Here, the aqueous solution contains at least one transition metal element constituting the lithium transition metal oxide. The raw material hydroxide generation step includes a nucleation stage in which a transition metal hydroxide is precipitated from an aqueous solution, and particle growth in which the transition metal hydroxide is grown in a state in which the pH of the aqueous solution is lower than that in the nucleation stage. Preferably including a step. The mixing step is a step of preparing an unfired mixture by mixing the transition metal hydroxide and the lithium compound. A baking process is a process of baking a mixture and obtaining a positive electrode active material. More preferably, the fired product is crushed and sieved after firing.

  Hereinafter, the method for producing the positive electrode active material will be illustrated more specifically. The positive electrode active material (typically porous hollow positive electrode active material particles) disclosed herein is, for example, at least one transition metal element contained in a lithium transition metal oxide constituting the active material (preferably, The transition metal hydroxide is precipitated under an appropriate condition from an aqueous solution containing all of the metal elements other than lithium contained in the oxide, and the transition metal hydroxide and the lithium compound are mixed and fired. It can be manufactured by the method to do.

  The embodiment of the method for producing a positive electrode active material will be described in detail by taking as an example the case of producing perforated hollow positive electrode active material particles made of a layered LiNiCoMn oxide. It is not intended to be limited to a positive electrode active material having a composition of (typically porous hollow positive electrode active material particles). Unless otherwise specified, the positive electrode active material is not limited to the manufacturing method disclosed herein.

(Raw material hydroxide production process)
The method for producing a positive electrode active material disclosed herein includes a step of supplying ammonium ions (NH ₄ ⁺ ) to an aqueous solution of a transition metal compound and precipitating transition metal hydroxide particles from the aqueous solution (raw material water). Oxide generation step). The solvent (aqueous solvent) constituting the aqueous solution is typically water, and may be a mixed solvent containing water as a main component. As the solvent other than water constituting the mixed solvent, an organic solvent (such as a lower alcohol) that can be uniformly mixed with water is preferable. The aqueous solution of the transition metal compound (hereinafter also referred to as “transition metal solution”) constitutes the lithium transition metal oxide according to the composition of the lithium transition metal oxide constituting the positive electrode active material particles as the production object. (in this case Ni, Co and Mn) is a transition metal element _{M T} contains at least one kind of (preferably all). For example, a transition metal solution containing one or more compounds capable of supplying Ni ions, Co ions, and Mn ions in an aqueous solvent is used. As the metal ion source compound, sulfates, nitrates, chlorides, and the like of the metals can be appropriately employed. For example, a transition metal solution having a composition in which nickel sulfate, cobalt sulfate and manganese sulfate are dissolved in an aqueous solvent (preferably water) can be preferably used.

The NH ₄ ⁺ may be supplied to the transition metal solution in the form of an aqueous solution (typically an aqueous solution) containing NH ₄ ⁺ , for example, and supplied by directly blowing ammonia gas into the transition metal solution. These supply methods may be used in combination. An aqueous solution containing NH ₄ ⁺ can be prepared, for example, by dissolving a compound (ammonium hydroxide, ammonium nitrate, ammonia gas, or the like) that can be an NH ₄ ⁺ source in an aqueous solvent. In this embodiment, NH ₄ ⁺ is supplied in the form of an aqueous ammonium hydroxide solution (ie, aqueous ammonia).

(Nucleation stage)
The raw material hydroxide generation step has a pH of 12 or more (typically pH 12 or more and 14 or less, such as pH 12.2 or more and 13 or less) and an NH ₄ ⁺ concentration of 25 g / L or less (typically 3 to 25 g / L). A step (nucleation step) of depositing a transition metal hydroxide from the transition metal solution under conditions may be included. The pH and NH ₄ ⁺ concentration can be adjusted by appropriately balancing the usage amounts of the ammonia water and the alkali agent (a compound having an action of tilting the liquid property to alkalinity). As the alkaline agent, for example, sodium hydroxide, potassium hydroxide and the like can be typically used in the form of an aqueous solution. In this embodiment, an aqueous sodium hydroxide solution is used. In addition, in this specification, the value of pH shall mean pH value on the basis of liquid temperature of 25 degreeC.

(Particle growth stage)
In the raw material hydroxide generation step, the transition metal hydroxide nuclei (typically particulate) precipitated in the nucleation stage are further reduced to a pH of less than 12 (typically pH 10 or more and less than 12, preferably pH 10). 11.8 or less (for example, pH 11 or more and 11.8 or less) and NH ₄ ⁺ concentration 1 g / L or more, preferably 3 g / L or more (typically 3 to 25 g / L) (growth stage) Can be included. Usually, the pH of the particle growth stage is 0.1 or more (typically 0.3 or more, preferably 0.5 or more, for example, about 0.5 to 1.5) lower than the pH of the nucleation stage. It is appropriate to do.

The pH and NH ₄ ⁺ concentration can be adjusted in the same manner as in the nucleation stage. This particle growth stage is performed so as to satisfy the pH and NH ₄ ⁺ concentration, and preferably at the pH, the NH ₄ ⁺ concentration is 20 g / L or less (eg, 1 to 20 g / L, typically 3 to 3). 20 g / L), more preferably 15 g / L or less (for example, 1 to 15 g / L, typically 3 to 10 g / L), so that transition metal hydroxides (here, Ni, Co and The precipitation rate of the composite hydroxide containing Mn is increased, and the raw material hydroxide particles (in other words, suitable for the formation of the positive electrode active material (typically the perforated hollow positive electrode active material particles) disclosed herein) , Raw material hydroxide particles that can easily form a fired product having a holed hollow structure.

The NH ₄ ⁺ concentration may be 7 g / L or less (for example, 1 to 7 g / L, more preferably 3 to 7 g / L). NH ₄ ⁺ concentration in the particle growth step, for example, may be a substantially the same level as NH ₄ ⁺ concentration in the nucleation stage, may be lower than the NH ₄ ⁺ concentration in the nucleation stage. In addition, the precipitation rate of the transition metal hydroxide is, for example, the transition metal ions contained in the liquid phase of the reaction liquid with respect to the total number of moles of transition metal ions contained in the transition metal solution supplied to the reaction liquid. It can be grasped by examining the transition of the total number of moles (total ion concentration).

  In each of the nucleation stage and the particle growth stage, the temperature of the reaction solution is preferably controlled so as to be a substantially constant temperature (for example, a predetermined temperature ± 1 ° C.) in a range of about 30 ° C. to 60 ° C. The temperature of the reaction liquid in the nucleation stage and the particle growth stage may be the same. Moreover, it is preferable to maintain the reaction liquid and the atmosphere in the reaction tank in a non-oxidizing atmosphere through the nucleation stage and the particle growth stage. Further, the total number of moles (total ion concentration) of Ni ions, Co ions and Mn ions contained in the reaction solution is set to, for example, about 0.5 to 2.5 mol / L through the nucleation stage and the particle growth stage. It is preferably about 1.0 to 2.2 mol / L. The transition metal solution may be replenished (typically continuously supplied) in accordance with the deposition rate of the transition metal hydroxide so that the total ion concentration is maintained. The amount of Ni ions, Co ions, and Mn ions contained in the reaction solution depends on the composition of the positive electrode active material particles that are the target (that is, the molar ratio of Ni, Co, and Mn in the LiNiCoMn oxide constituting the active material particles). A corresponding quantitative ratio is preferred.

(Mixing process)
In this embodiment, the transition metal hydroxide particles (here, composite hydroxide particles containing Ni, Co and Mn) produced by the above-described method are separated from the reaction solution, washed and dried. Then, the transition metal hydroxide particles and the lithium compound are mixed at a desired quantitative ratio to prepare an unfired mixture (mixing step). In this mixing step, typically, the quantity ratio corresponding to the composition of the positive electrode active material particles as the target object (that is, the molar ratio of Li, Ni, Co, and Mn in the LiNiCoMn oxide constituting the active material particles). , Li compound and transition metal hydroxide particles are mixed. As the lithium compound, Li compounds that can be dissolved by heating and become oxides, such as lithium carbonate and lithium hydroxide, can be preferably used.

(Baking process)
And the said mixture is baked and positive electrode active material particle is obtained (baking process). This firing step is typically performed in an oxidizing atmosphere (for example, in the air (air atmosphere)). The firing temperature in this firing step can be set to 700 ° C. to 1100 ° C., for example. It is preferable that the maximum baking temperature be 800 ° C or higher (preferably 800 ° C to 1100 ° C, for example, 800 ° C to 1050 ° C). According to the maximum firing temperature within this range, the sintering reaction of the primary particles of the lithium transition metal oxide (preferably Ni-containing Li oxide, here LiNiCoMn oxide) can proceed appropriately.

  In a preferred embodiment, the mixture is calcined at a temperature T1 of 700 ° C. to 900 ° C. (that is, 700 ° C. ≦ T1 ≦ 900 ° C., for example, 700 ° C. ≦ T1 ≦ 800 ° C., typically 700 ° C. ≦ T1 <800 ° C.). A second firing step, and a result obtained through the first firing step is fired at a temperature T2 of 800 ° C. to 1100 ° C. (that is, 800 ° C. ≦ T2 ≦ 1100 ° C., for example, 800 ° C. ≦ T2 ≦ 1050 ° C.) Firing step. This makes it possible to more efficiently form positive electrode active material particles having a perforated hollow structure. T1 and T2 are preferably set so that T1 <T2.

   The first baking stage and the second baking stage may be continued (for example, after the mixture is held at the first baking temperature T1, the temperature is subsequently raised to the second baking temperature T2 and held at the temperature T2. Alternatively, after being held at the first firing temperature T1, it may be cooled once (for example, cooled to room temperature) and, if necessary, crushed and sieved before being subjected to the second firing stage. .

  In the technology disclosed herein, the first firing stage is a temperature range in which the sintering reaction of the target lithium transition metal oxide proceeds and is lower than the melting point and lower than the second firing stage. This can be understood as the stage of firing at T1. In addition, the second firing stage is grasped as a stage in which the sintering reaction of the target lithium transition metal oxide proceeds and the firing is performed at a temperature T2 that is lower than the melting point and higher than the first firing stage. be able to. It is preferable to provide a temperature difference of 50 ° C. or higher (typically 100 ° C. or higher, for example, 150 ° C. or higher) between T1 and T2.

Further, the ratio of the hollow portion in the apparent cross-sectional area of the positive electrode active material is 15% or more (more preferably 20% or more, and further preferably 23% or more), and the thickness of the shell portion of the positive electrode active material In order to more stably obtain a thin positive electrode active material having a thickness of 3.0 μm or less (more preferably 2.2 μm or less), for example, in the step of depositing transition metal hydroxide from a transition metal solution (nucleation step) pH or NH ₄ ⁺ concentration, and may the pH or NH ₄ ⁺ concentration in the step of growing the nuclei of the transition metal hydroxide is precipitated at the nucleation stage (particle growth stage) appropriately adjusted.

In carrying out the technology disclosed herein, a precursor hydroxide suitable for forming a positive electrode active material having a hollow structure (preferably a porous structure having pores) by suppressing the ammonia concentration in the particle growth stage as described above. Although it is not necessary to clarify the reason why is obtained, for example, the following can be considered. That is, for example, the following equilibrium reaction occurs in the mixed solution (reaction solution). M ₁ in the following formulas 1 and 2 is a transition metal (for example, Ni).

Here, when the ammonia concentration in the reaction solution is lowered, the equilibrium of Formula 1 shifts to the left and the concentration of M ₁ ²⁺ increases, so the balance of Formula 2 shifts to the right and M ₁ (OH) ₂ is generated. Is promoted. In other words, M ₁ (OH) ₂ is likely to precipitate. In such a situation where M ₁ (OH) ₂ is likely to precipitate, M ₁ (OH) ₂ is mainly precipitated because of the transition metal hydroxide already precipitated (nuclei generated in the nucleation stage, or M ₁ (OH) ₂ that occurs in the vicinity of the outer surface of the transition metal hydroxide particles in the course of the grain growth stage and precipitates inside the precipitate is reduced. As a result, precursor hydroxide particles having a structure in which the internal density is lower than the density of the outer surface portion (transition metal hydroxide particles suitable for forming positive active material particles having a hollow structure, It can be assumed that the precursor particles of the particles are formed.

When the precursor hydroxide particles having such a structure are mixed with a lithium compound and fired, the inside of the particles having a low density is taken into the vicinity of the outer surface where the density is high and the mechanical strength is high. It can be sintered. For this reason, as shown in FIG. 5, the shell 115 of the positive electrode active material particle 110 is formed, and the large hollow portion 116 is formed. Furthermore, when a crystal grows during sintering, a through hole 118 penetrating the shell 115 is formed in a part of the shell 115. Thereby, it is considered that the positive electrode active material particles 110 having the shell portion 115, the hollow portion 116, and the through hole 118 are formed. On the other hand, if the ammonia concentration in the particle growth stage is too high, the precipitation rate of M ₁ (OH) ₂ becomes small, so the difference between the precipitation amount in the vicinity of the outer surface and the precipitation amount in the interior becomes small, and the precursor of the above structure It is presumed that hydroxide particles are hardly formed.

In addition to M _T (that is, at least one of Ni, Co, and Mn), the positive electrode active material is one or more other elements M _A and M as additional constituent elements (addition elements). _B (e.g. W, Cr, Mo, Zr, Mg, Ca, Na, Fe, Zn, Si, Sn, Al, B, F) in the case of containing includes a precursor hydroxide containing _{M T,} M a compound containing at least one of _a and M _B, by firing a mixture of a lithium compound (dry mixing method) can be prepared. Alternatively, it may be prepared by firing a mixture of a precursor hydroxide and the lithium compound having a composition comprising at least one of M _T and M _A and M _B. In the technique disclosed here, a method of calcining a mixture of a precursor hydroxide containing M _T and at least one of M _A and M _B and a lithium compound can be preferably employed. And the M _T, the precursor hydroxides and at least one of M _A and M _B are, for example, a method of producing the precursor hydroxide from the reaction solution containing these (wet method (a coprecipitation method)) Can be preferably prepared. According to this embodiment, M _A in positive electrode active _material, the distribution of M _B, it is possible to obtain a positive electrode active material localized agglomeration is prevented. For example, in comparison with the positive electrode active material obtained by the above dry mixing method, the surface of the primary particles of the entire positive electrode active material or the active materials, the more uniformly M _A, the positive electrode active material was present M _B element be able to. The amount of M _A, M _B may be the target compound serving composition of the positive electrode active material particles (i.e., M _A contained in the active material _particles, the molar ratio of M _B) generally corresponds to the amount ratio.

  In addition to the hollow structure positive electrode active material disclosed here, the positive electrode may include other conventionally known positive electrode active materials (for example, a solid structure positive electrode active material) as the positive electrode active material. However, since the effect of the present invention is to solve the problem caused by using the positive electrode active material having the hollow structure, the proportion of the other conventionally known positive electrode active material is 50% by mass of the entire positive electrode active material. It is desirable to set the following (for example, 30% by mass or less, typically 10% by mass or less). The positive electrode active material can be substantially made of the positive electrode active material having the hollow structure.

<Additives>
In addition to the positive electrode active material, the positive electrode mixture layer may contain additives such as a conductive material and a binder (binder) as necessary. As the conductive material, a conductive powder material such as carbon powder or carbon fiber is preferably used. As the carbon powder, various carbon blacks such as acetylene black, furnace black, ketjen black, and graphite powder are preferable. In addition, conductive fibers such as carbon fibers and metal fibers, metal powders such as copper and nickel, and organic conductive materials such as polyphenylene derivatives may be included singly or as a mixture of two or more. it can.

  Examples of the binder include various polymer materials. For example, when the positive electrode mixture layer is formed using an aqueous composition (a composition using water or a mixed solvent containing water as a main component as a dispersion medium for the positive electrode active material particles), water is used as the binder. Polymer materials that are soluble or dispersible in water (water-soluble or water-dispersible) can be preferably employed. Examples of water-soluble or water-dispersible polymer materials include cellulose polymers such as carboxymethyl cellulose (CMC); fluorocarbon resins such as polyvinyl alcohol (PVA); polytetrafluoroethylene (PTFE); vinyl acetate polymers; styrene butadiene rubber Rubbers such as (SBR) and acrylic acid-modified SBR resin (SBR latex);

  Alternatively, when the positive electrode mixture layer is formed using a solvent-based composition (a composition in which the dispersion medium of the positive electrode active material particles is mainly an organic solvent), polyvinylidene fluoride (PVDF), polyvinylidene chloride (PVDC) Polymer materials such as vinyl halide resins such as); polyalkylene oxides such as polyethylene oxide (PEO); and the like can be used. Such a binder may be used alone or in combination of two or more. In addition, the polymer material illustrated above may be used as a thickener and other additives in the composition for forming a positive electrode mixture layer, in addition to being used as a binder.

<Combination ratio>
The proportion of the positive electrode active material in the positive electrode mixture layer is more than about 50% by mass, and preferably about 70% to 97% by mass (for example, 75% to 95% by mass). Further, the ratio of these additives in the positive electrode mixture layer is not particularly limited, but the ratio of the conductive material is preferably about 2% by mass to 20% by mass (for example, 3% by mass to 18% by mass). The ratio of the material is preferably about 1% by mass to 10% by mass (for example, 2% by mass to 7% by mass).

<Method for producing positive electrode>
A method for manufacturing the positive electrode as described above is not particularly limited, and a conventional method can be appropriately employed. For example, it can be produced by the following method. First, a positive electrode active material, if necessary, a conductive material, a binder, etc. are mixed with an appropriate solvent (aqueous solvent, non-aqueous solvent or a mixed solvent thereof) to form a paste-like or slurry-like positive electrode mixture layer A composition is prepared. The mixing operation can be performed using, for example, a suitable kneader (planetary mixer, homodisper, clear mix, fill mix, etc.). As a solvent used for preparing the composition, both an aqueous solvent and a non-aqueous solvent can be used. The aqueous solvent is not particularly limited as long as it is water-based as a whole, and water or a mixed solvent mainly composed of water can be preferably used. Preferable examples of the non-aqueous solvent include N-methyl-2-pyrrolidone (NMP), methyl ethyl ketone, toluene and the like.

  The composition prepared in this manner is applied to a positive electrode current collector, the solvent is volatilized by drying, and then compressed (pressed). As a method for applying the composition to the positive electrode current collector, a technique similar to a conventionally known method can be appropriately employed. For example, the composition can be suitably applied to the positive electrode current collector by using an appropriate application device such as a slit coater, a die coater, a gravure coater, or a comma coater. Moreover, when drying a solvent, it can dry favorably by using natural drying, a hot air, low-humidity air, a vacuum, infrared rays, far infrared rays, and an electron beam individually or in combination. Furthermore, as a compression method, a conventionally known compression method such as a roll press method or a flat plate press method can be employed. In adjusting the thickness, the thickness may be measured with a film thickness measuring instrument, and the press pressure may be adjusted to compress the film a plurality of times until a desired thickness is obtained. In this way, a positive electrode in which the positive electrode mixture layer is formed on the positive electrode current collector is obtained.

The basis weight per unit area of the positive electrode mixture layer on the positive electrode current collector (the coating amount in terms of solid content of the composition for forming the positive electrode mixture layer) is not particularly limited, but a sufficient conductive path From the viewpoint of securing a (conduction path), it is 3 mg / cm ² or more (for example, 5 mg / cm ² or more, typically 6 mg / cm ² or more) per side of the positive electrode current collector, and 45 mg / cm ² or less (for example, 28 mg / cm ² or less, typically 15 mg / cm ² or less). The density of the positive electrode mixture layer is not particularly limited, but is 1.0 g / cm ^{3 to} 3.8 g / cm ³ (for example, 1.5 g / cm ^{3 to} 3.0 g / cm ³ , typically 1.8 g / cm 3). ^{3 to} 2.4 g / cm ³ ).

≪Negative electrode≫
As the negative electrode current collector constituting the negative electrode (typically, the negative electrode sheet), a conductive member made of a metal having good conductivity is preferably used as in the case of a conventional lithium secondary battery. As such a conductive member, for example, copper or an alloy containing copper as a main component can be used. The shape of the negative electrode current collector can be different depending on the shape of the battery and is not particularly limited, and may be various forms such as a rod shape, a plate shape, a sheet shape, a foil shape, and a mesh shape. The thickness of the negative electrode current collector is not particularly limited, and can be about 5 μm to 30 μm.

<Negative electrode mixture layer>
The negative electrode mixture layer includes a negative electrode active material that can occlude and release Li ions serving as charge carriers. There is no restriction | limiting in particular in a composition and a shape of a negative electrode active material, The 1 type (s) or 2 or more types of the material conventionally used for a lithium secondary battery can be used. Examples of such a negative electrode active material include carbon materials that are generally used in lithium secondary batteries. Representative examples of the carbon material include graphite carbon (graphite) and amorphous carbon. A particulate carbon material (carbon particles) containing a graphite structure (layered structure) at least partially is preferably used. Of these, the use of a carbon material mainly composed of natural graphite is preferred. The natural graphite may be a spheroidized graphite. Alternatively, a carbonaceous powder having a graphite surface coated with amorphous carbon may be used. In addition, as the negative electrode active material, it is also possible to use oxides such as lithium titanate, simple substances such as silicon materials and tin materials, alloys, compounds, and composite materials using the above materials in combination. The proportion of the negative electrode active material in the negative electrode mixture layer is more than about 50% by mass, and about 90% to 99% by mass (for example, 95% to 99% by mass, typically 97% to 99% by mass). Preferably there is.

  In addition to the negative electrode active material, the negative electrode mixture layer requires one or more binders, thickeners, and other additives that can be blended in the negative electrode mixture layer of a typical lithium secondary battery. It can be contained accordingly. Examples of the binder include various polymer materials. For example, what can be contained in the positive electrode mixture layer can be preferably used for an aqueous composition or a solvent-based composition. Such a binder may be used as a thickener and other additives in the composition for forming a negative electrode mixture layer, in addition to being used as a binder. The ratio of these additives in the negative electrode mixture layer is not particularly limited, but is approximately 0.8% by mass to 10% by mass (for example, approximately 1% by mass to 5% by mass, typically 1% by mass to 3% by mass). It is preferable that

  The method for producing the negative electrode is not particularly limited, and a conventional method can be employed. For example, it can be produced by the following method. First, a negative electrode active material is mixed with a binder or the like in the appropriate solvent (aqueous solvent, organic solvent, or mixed solvent thereof) to prepare a paste or slurry-like composition for forming a negative electrode mixture layer. The composition prepared in this manner is applied to the negative electrode current collector, the solvent is volatilized by drying, and then compressed (pressed). Thus, a negative electrode mixture layer can be formed on a negative electrode current collector using the composition, and a negative electrode provided with the negative electrode mixture layer can be obtained. Note that the mixing, coating, drying, and compression methods can employ the same means as in the above-described production of the positive electrode.

The basis weight per unit area of the negative electrode composite material layer on the negative electrode current collector (the coating amount in terms of solid content of the composition for forming the negative electrode composite material layer) is not particularly limited, but sufficient conductive paths From the viewpoint of securing a (conduction path), it is 2 mg / cm ² or more (for example, 3 mg / cm ² or more, typically 4 mg / cm ² or more) per side of the negative electrode current collector, and 40 mg / cm ² or less (for example, 22 mg / cm ² or less, typically 10 mg / cm ² or less). The density of the negative electrode mixture layer is not particularly limited, but is 0.5 g / cm ^{3 to} 3.0 g / cm ³ (for example, 0.7 g / cm ^{3 to} 2.0 g / cm ³ , typically 0.8 g / cm 3). ^{3 to} 1.4 g / cm ³ ).

≪Capacitance ratio between positive electrode and negative electrode≫
Although not particularly limited, the ratio (C _N / C _P ) of the initial charge capacity (C _N ) of the negative electrode to the initial charge capacity (C _P ) of the positive electrode is usually 1.1 to 2.1, for example. It is suitable and it is preferable to set it as 1.2-2.0. If C _N / C _P is too small, inconveniences such as easy deposition of metallic lithium may occur depending on the use conditions of the battery (for example, during rapid charging). When C _N / C _P is too large, the energy density of the battery may be easily lowered.

≪Separator≫
The separator (separator sheet) disposed so as to separate the positive electrode and the negative electrode may be a member that insulates the positive electrode mixture layer and the negative electrode mixture layer and allows the electrolyte to move. As said separator, the thing similar to the sheet | seat used as a separator in the conventional lithium secondary battery can be used. For example, a sheet mainly composed of a thermoplastic resin such as polyolefin (polyethylene (PE), polypropylene (PP), etc.), polyester, polyamide or the like can be preferably used. As a preferred example, a sheet having a single-layer structure or a multilayer structure (polyolefin-based sheet) mainly composed of one or more kinds of polyolefin-based resins can be given. For example, a PE sheet, a PP sheet, a sheet having a three-layer structure (PP / PE / PP structure) in which PP layers are laminated on both sides of the PE layer, and the like can be suitably used. The PE may be any polyethylene generally referred to as high-density polyethylene (HDPE), low-density polyethylene (LDPE), or linear (linear) low-density polyethylene (LLDPE), or a mixture thereof. May be. Moreover, the said separator can also contain additives, such as various plasticizers and antioxidant, as needed.

  As a separator in the technique disclosed herein, a thermoplastic resin (for example, polyolefin) whose shutdown temperature is set to about 80 ° C. to 140 ° C. (for example, 110 ° C. to 140 ° C., typically 120 ° C. to 135 ° C.). Resin) porous sheet can be preferably employed. Since the shutdown temperature is sufficiently lower than the heat resistant temperature of the battery (typically about 200 ° C. or higher), the shutdown function can be exhibited at an appropriate timing. In addition, even if the separator is thermally contracted or perforated at a shutdown temperature or higher, a heat-resistant barrier layer is provided between the positive and negative electrodes (typically, between the positive electrode and the separator). The insulation between them can be maintained appropriately.

  As the resin layer constituting the separator having a single layer structure or a multilayer structure, for example, a uniaxially stretched or biaxially stretched porous resin film can be suitably used. Among these, a porous resin film uniaxially stretched in the longitudinal direction is particularly preferable because it has an appropriate strength and has little heat shrinkage in the width direction. When a separator having a uniaxially stretched porous resin film is used, thermal contraction in the longitudinal direction can be suppressed in a mode in which the separator is wound together with a long sheet-like positive electrode and negative electrode. Therefore, the porous resin film uniaxially stretched in the longitudinal direction is particularly suitable as one element of the separator constituting the wound electrode body.

The porosity (porosity) of the separator is preferably about 20 to 60%, and more preferably about 30 to 50%, for example. If the porosity of the separator is too large, the strength may be insufficient or the heat shrinkage may be significant. On the other hand, when the porosity is too small, the amount of the electrolyte solution that can be held in the separator is reduced, the ionic conductivity is lowered, and the high-rate charge / discharge characteristics may be lowered. The porosity (porosity) of the separator can be calculated by the following method. The apparent volume occupied by the separator of the unit area (surface area) is V1 [cm ³ ], and the mass of the unit area separator is W [g]. The ratio between the mass W and the true density ρ [g / cm ³ ] of the resin material constituting the separator, that is, W / ρ is V0. Note that V0 is a volume occupied by a dense body of resin material having a mass W. The porosity (porosity) of the separator can be calculated from [(V1−V0) / V1] × 100. The porosity (porosity) of the separator can be adjusted by the material of the resin layer, the stretching strength, and the like.

  If the average pore size of the separator is too small, the ionic conductivity may decrease, and the high rate charge / discharge characteristics may tend to decrease. If the average pore diameter is too large, when a heat-resistant barrier layer described later is formed on the separator, the filler constituting the heat-resistant barrier layer will enter the pores of the separator too much, resulting in ion conductivity and high-rate charge / discharge characteristics. May tend to decrease. The average pore diameter of the separator has a correlation with the air permeability, and by defining this air permeability, the average pore diameter can be defined in a pseudo manner. Here, “air permeability” refers to air resistance (Gurley) and can be measured by the method defined in JIS P8117. A separator that satisfies the above air permeability (Gurley number) of about 100 to 1000 seconds / 100 mL (for example, 200 to 600 seconds / 100 mL) can be preferably used.

  The thickness of the separator is not particularly limited, but is preferably about 5 μm to 40 μm (for example, 10 μm to 30 μm, typically 15 μm to 25 μm). When the thickness of the separator is within the above range, the ion conductivity of the separator becomes better, and film breakage is less likely to occur. Note that the thickness of the separator can be obtained by analyzing an image taken by an SEM.

≪Heat-resistant barrier layer≫
The heat-resistant barrier layer disposed between the positive electrode and the separator does not soften or melt even when the battery generates heat and reaches a high temperature (eg, 150 ° C. or higher, typically 300 ° C. or higher). It is possible to maintain the property (slight deformation is acceptable). In addition, when forming a heat-resistant interruption | blocking layer on a separator, a heat-resistant interruption | blocking layer may also have a higher softening point or melting | fusing point than a separator.

(Filler)
The filler that can be the main component of the heat-resistant barrier layer may be either an organic filler or an inorganic filler, but it is preferable to use an inorganic filler in consideration of heat resistance, dispersibility, and stability. The inorganic filler is not particularly limited. For example, inorganic oxides such as alumina, boehmite, silica, titania, zirconia, calcia, magnesia, and iron oxide, inorganic nitrides such as aluminum nitride, carbonates such as magnesium carbonate, and barium sulfate. Such as sulfate, magnesium chloride, fluoride such as barium fluoride, covalent crystals such as silicon, talc, clay, mica, bentonite, montmorillonite, zeolite, apatite, kaolin, mullite, sericite, etc. It may be a mineral-based material or an artificial product thereof. These can be used alone or in combination of two or more. Among these, alumina, boehmite, silica, titania, zirconia, calcia, and magnesia are preferable, and boehmite and alumina are particularly preferable because of high electrochemical stability and excellent heat resistance and mechanical strength.

The form of the filler is not particularly limited, and may be, for example, a particle shape, a fiber shape, a plate shape (flake shape), or the like. The average particle diameter of the filler is not particularly limited, but is suitably 0.1 μm to 15 μm (for example, 0.1 μm to 5 μm, typically 0.2 μm to 1.5 μm) in consideration of dispersibility and the like. . The average particle size of the filler may be employed the D _50.

(Additives)
The heat-resistant barrier layer preferably also contains an additive such as a binder. When the composition for forming a heat-resistant barrier layer is an aqueous solvent (a solution using water or a mixed solvent containing water as a main component as a dispersion medium for the binder), the binder is dispersed in an aqueous solvent or Soluble polymers can be used. Examples of the polymer that is dispersed or dissolved in the aqueous solvent include acrylic resins. Acrylic resins include acrylic acid, methacrylic acid, acrylamide, methacrylamide, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, methyl methacrylate, 2-ethylhexyl acrylate and butyl acrylate. Coalescence is preferably used. Or the copolymer which superposed | polymerized 2 or more types of the said monomer may be sufficient. Further, a mixture of two or more of the above homopolymers and copolymers may be used. In addition to the acrylic resin described above, styrene butadiene rubber (SBR), acrylic acid-modified SBR resin (SBR latex), rubber such as gum arabic; polyolefin resin such as polyethylene (PE); carboxymethylcellulose (CMC), Cellulose polymers such as methyl cellulose (MC); polyvinyl alcohol (PVA); fluorine resins such as polytetrafluoroethylene (PTFE); vinyl acetate polymers; polyalkylene oxides such as polyethylene oxide (PEO); it can. These polymers can be used alone or in combination of two or more. Of these, acrylic resins, SBR, polyolefin resins, and CMC are preferable. These water-based binders are preferable in that they do not react or harden with moisture in the atmosphere, and thus the extensibility of the heat-resistant barrier layer can be easily adjusted (for example, without performing moisture management during production).

  In the case where the heat-resistant barrier layer forming composition is a solvent-based solvent (a solution in which the binder dispersion medium is mainly an organic solvent), the binder is a polymer dispersed or dissolved in the solvent-based solvent. Can be used. Examples of the polymer that is dispersed or dissolved in the solvent-based solvent include vinyl halide resins such as polyvinylidene fluoride (PVDF). As the polyvinylidene fluoride, a homopolymer of vinylidene fluoride is preferably used. Furthermore, the polyvinylidene fluoride may be a copolymer of a vinyl monomer copolymerizable with vinylidene fluoride. Examples of vinyl monomers copolymerizable with vinylidene fluoride include hexafluoropropylene, tetrafluoroethylene, and ethylene trichloride fluoride. Alternatively, polytetrafluoroethylene (PTFE), polyacrylonitrile, polymethyl methacrylate, or the like is preferably used as a polymer that is dispersed or dissolved in a solvent-based solvent. These may be used alone or in combination of two or more. These solvent-based binders are preferable in that the extensibility of the heat-resistant barrier layer can be suitably improved. However, since the solvent-based binder can be cured by reacting with moisture in the atmosphere, it is necessary to perform moisture management during production.

The form of the binder is not particularly limited, and a particulate (powdered) form may be used as it is, or a solution or emulsion prepared may be used. Two or more binders may be used in different forms. When the particulate binder is used, the average particle diameter (the above-mentioned average particle diameter D ₅₀ ) is, for example, about 0.09 μm to 0.15 μm. In addition to the function as a binder, the said binder may be used in order to exhibit the function as a thickener and other additives of the composition for heat resistant barrier layer formation.

(Mixing ratio)
The proportion of the filler (typically inorganic filler) in the entire heat-resistant barrier layer is not particularly limited, but is approximately 90% by mass or more (for example, 92% to 99.5% by mass, typically 95% to 99% by mass). % By mass). Further, when the heat-resistant barrier layer contains additives such as a binder and a thickener, the proportion of the additive in the heat-resistant barrier layer is approximately 10% by mass or less (for example, 0.5% by mass to 8% by mass). , Typically 1% by mass to 5% by mass). When the proportion of the filler, if necessary, the binder and other additives is within the above range, the anchoring property of the heat-resistant barrier layer and the strength (shape retention) of the heat-resistant barrier layer itself are improved. Moreover, it becomes easy to adjust the porosity of the heat-resistant barrier layer to a favorable range, and the ion conductivity tends to be further improved. Furthermore, when the heat-resistant barrier layer is formed on the separator, it is easy to adjust the strength and elongation of the separator to a suitable range.

(Characteristics of heat-resistant barrier layer)
The porosity (porosity) of the heat-resistant barrier layer is not particularly limited, but it is 40% or more (for example, 45% or more, typically 50% or more) from the viewpoint of improving the nonaqueous electrolyte retention and ion conductivity. Preferably there is. In addition, the porosity (porosity) is 75% or less (for example, 70% or less, typically 65% or less) from the viewpoint of suppressing heat shrinkage and obtaining a strength that does not cause defects such as cracks and peeling. It is preferable that The porosity (porosity) of the heat-resistant barrier layer can be calculated by the same method as the calculation of the separator porosity (porosity). In that case, the mass W of the heat-resistant barrier layer can be measured, for example, as follows. That is, a separator or positive electrode on which a heat-resistant blocking layer is formed is cut out to a predetermined area to obtain a sample, and its mass is measured. Next, the mass of the heat-resistant barrier layer having the predetermined area is calculated by subtracting the mass of the separator or positive electrode having the predetermined area from the mass of the sample. The mass W [g] of the heat-resistant barrier layer can be calculated by converting the mass of the heat-resistant barrier layer thus calculated per unit area. The porosity (porosity) of the heat-resistant barrier layer can be adjusted by the constituent components, the blending ratio thereof, the coating method, the drying method and the like.

  The thickness of the heat-resistant barrier layer is not particularly limited, but is more preferably about 1 μm to 12 μm (for example, 2 μm to 10 μm, typically 3 μm to 8 μm). When the thickness of the heat-resistant barrier layer is within the above range, the short-circuit prevention effect and the non-aqueous electrolyte retention are improved. Moreover, when the said thickness is 2 micrometers or more, when a separator fuse | melts, it can interrupt | block suitably that the molten material permeates into a positive electrode. Furthermore, when a heat-resistant barrier layer is provided on the separator, it is easy to adjust the strength and elongation of the separator within a suitable range. The thickness of the heat-resistant barrier layer can be obtained by analyzing an image photographed by SEM.

(Method for forming heat-resistant barrier layer)
The method for forming the heat-resistant barrier layer disclosed herein is not particularly limited, and for example, it can be formed by the following method. First, the above-described filler, if necessary, a binder and other additives are mixed and dispersed in an appropriate solvent to prepare a paste-like (or slurry-like) heat-resistant barrier layer forming composition. Mixing and dispersing operations can be performed using an appropriate kneader such as a disper mill, a clear mix, a fill mix, a ball mill, a homodisper, or an ultrasonic disperser. The blending ratio of the obtained paste-like (or slurry-like) composition for forming a heat-resistant barrier layer, if necessary, the binder and other additives is the above-mentioned heat-resistant barrier layer in terms of solid content. It can be made the same as the ratio of each component occupying.

  Examples of the solvent used in the composition for forming a heat-resistant barrier layer include water or a mixed solvent mainly composed of water. As the solvent other than water constituting the mixed solvent, one or more organic solvents (lower alcohol such as ethanol, lower ketone, etc.) that can be uniformly mixed with water can be appropriately selected and used. Alternatively, one organic solvent such as N-methyl-2-pyrrolidone (NMP), pyrrolidone, methyl ethyl ketone, methyl isobutyl ketone, ixahexanone, toluene, dimethylformamide, dimethylacetamide, or a combination of two or more. It may be used. Although the content rate of the solvent in the composition for heat resistant blocking layer formation is not specifically limited, It may be 30 mass%-90 mass% (for example, 40 mass%-60 mass%) of the whole composition.

  Next, an appropriate amount of the obtained paste-like (or slurry-like) heat-resistant barrier layer-forming composition is applied to at least one surface of the separator sheet and the positive electrode sheet, and further dried, whereby a heat-resistant barrier layer is formed. Can be formed. The operation of applying the heat-resistant barrier layer forming composition to at least one surface of the separator sheet and the positive electrode sheet can be used without any particular limitation on conventional general application means. For example, by using a suitable coating apparatus (gravure coater, slit coater, die coater, comma coater, dip coat, etc.) A predetermined amount of the composition for forming a heat-resistant barrier layer is applied to one surface) to a uniform thickness. Then, the solvent in the composition for forming a heat resistant barrier layer is removed by drying the coated product by a suitable drying means. For example, when the heat-resistant barrier layer is formed on the separator sheet, the above drying is performed at a temperature lower than the melting point of the material constituting the separator sheet, for example, 110 ° C. or less (typically 30 to 80 ° C.). obtain. Or you may hold | maintain under low temperature pressure reduction, and may make it dry. By removing the solvent from the heat-resistant barrier layer forming composition, a heat-resistant barrier layer containing a filler as a main component can be formed. In this way, an electrode body in which a heat-resistant barrier layer is disposed between the positive electrode and the separator can be obtained.

≪Nonaqueous electrolyte≫
As the non-aqueous solvent and the supporting salt constituting the non-aqueous electrolyte injected into the lithium secondary battery, those conventionally used for lithium secondary batteries can be used without any particular limitation. Such a non-aqueous electrolyte is typically an electrolytic solution having a composition in which a supporting salt is contained in a suitable non-aqueous solvent. Examples of the non-aqueous solvent include ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), 1,2-dimethoxyethane, 1,2- Diethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dioxane, 1,3-dioxolane, diethylene glycol dimethyl ether, ethylene glycol dimethyl ether, acetonitrile, propionitrile, nitromethane, N, N-dimethylformamide, dimethyl sulfoxide, sulfolane, γ-butyrolactone These may be used alone or in combination of two or more. Of these, a mixed solvent of ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) is preferable.

Examples of the supporting salt include LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) _3. One or more of lithium compounds (lithium salts) such as LiI can be used. The concentration of the supporting salt is not particularly limited, but is approximately 0.1 mol / L to 5 mol / L (for example, 0.5 mol / L to 3 mol / L, typically 0.8 mol / L to 1.5 mol / L). Concentration.

The non-aqueous electrolyte may contain an optional additive as necessary as long as the object of the present invention is not significantly impaired. The additive is used for one or more purposes such as, for example, improving battery output performance, improving storage stability (suppressing capacity reduction during storage, etc.), improving cycle characteristics, improving initial charge / discharge efficiency, etc. Can be done. Examples of preferable additives include fluorophosphate (preferably difluorophosphate, for example, lithium difluorophosphate represented by LiPO ₂ F ₂ ), lithium bisoxalate borate (LiBOB), and the like. The concentration of each additive in the non-aqueous electrolyte is usually 0.20 mol / L or less (typically 0.005 to 0.20 mol / L), for example, 0.10 mol / L or less ( Typically, it can be 0.01 to 0.10 mol / L). As a preferable embodiment, a nonaqueous electrolytic solution containing both LiPO ₂ F ₂ and LiBOB at a concentration of 0.01 to 0.05 mol / L (for example, 0.025 mol / L, respectively) can be given.

  As described above, the lithium secondary battery having such a configuration is not only excellent in output characteristics at low SOC, but also excellent in thermal stability, and thus can be used as a secondary battery for various applications. For example, as shown in FIG. 7, the lithium secondary battery 100 is mounted on a vehicle 1 such as an automobile and can be suitably used as a power source for a drive source such as a motor that drives the vehicle 1. Therefore, the present invention provides a vehicle (typically an automobile, particularly a hybrid automobile (HV), a plug-in hybrid automobile (including a battery pack typically formed by connecting a plurality of series-connected batteries) 100 as a power source. PHV), an electric vehicle (EV), a vehicle equipped with an electric motor such as a fuel cell vehicle) 1 can be provided.

  Next, some examples relating to the present invention will be described, but the present invention is not intended to be limited to those shown in the examples. In the following description, “parts” and “%” are based on mass unless otherwise specified.

<Example 1>
[Preparation of positive electrode active material A having a hollow structure]
Nickel sulfate (NiSO ₄ ), cobalt sulfate (CoSO ₄ ), manganese sulfate (MnSO ₄ ) and zirconium sulfate (ZrSO ₄ ) are dissolved in water, and the molar ratio of Ni: Co: Mn is about 0.34: 0. An aqueous solution aq _A having a ratio of 33: 0.33, a molar ratio of Zr to all transition metal elements of 0.002, and a total concentration of Ni, Co and Mn of 1.8 mol / L was prepared. Further, ammonium paratungstate (5 (NH ₄ ) ₂ O · 12WO ₃ ) was dissolved in water to prepare an aqueous solution aq _B (W aqueous solution) having a W concentration of 0.1 mol / L. About half the volume of water was placed in a reaction vessel equipped with a stirrer and a nitrogen introduction tube, and heated to 40 ° C. with stirring. Appropriate amounts of 25% (mass basis) sodium hydroxide aqueous solution and 25% (mass basis) ammonia water were added respectively while maintaining the space in the reaction vessel in a non-oxidizing atmosphere with an oxygen concentration of 2.0% under a nitrogen stream. Then, an alkaline aqueous solution (NH ₃ · NaOH aqueous solution) having a pH of 12.0 based on a liquid temperature of 25 ° C. and an ammonia concentration in the liquid phase of 20 g / L was prepared. By supplying the aqueous solution aq _A , the aqueous solution aq _B , the aqueous solution aq _B , the 25% aqueous sodium hydroxide solution, and the 25% aqueous ammonia prepared at the above rate to the alkaline aqueous solution in the reaction vessel, respectively, Hydroxides were crystallized from the reaction solution while maintaining the pH at 12.0 or higher (specifically, pH 12.0 to 14.0) and an ammonia concentration of 20 g / L (nucleation stage).

Subsequently, the supply rate of each liquid to the reaction tank is adjusted to adjust the reaction liquid to a pH of less than 12.0 (specifically, to a pH of 10.5 to 11.9, and a liquid phase ammonia concentration of 1 to 20 g / The particle growth reaction of the nuclei generated above was performed while controlling the concentration to a predetermined concentration in the range of L. (Particle growth stage) The product was removed from the reaction vessel, washed with water, and dried to obtain (Ni + Co + Mn): Zr: A composite hydroxide (precursor hydroxide) having a molar ratio of W of 1000.2 :: 0.5 was obtained, and this precursor hydroxide was subjected to heat treatment at 150 ° C. for 12 hours in an air atmosphere. Thereafter, Li ₂ CO ₃ (lithium source) and the precursor hydroxide were mixed so that the molar ratio of Li: (Ni + Co + Mn) (ie, m _Li : m _T ) was 1.14: 1. (Mixing step) This unfired mixture was removed from the atmosphere. Baked for 7 hours at 950 ° C. At this time, the rate of temperature increase reaching 950 ° C. was 5 ° C./minute, and then the fired product was cooled, crushed and sieved. A positive electrode active material A having an average composition represented by Li _1.14 Ni _0.34 Co _0.33 Mn _0.33 Zr _0.002 W _0.005 O ₂ was obtained. The particles were confirmed to have a hollow structure by SEM image observation, the average particle diameter (D ₅₀ ) of the secondary particles was 5.4 μm, and the particle diameter (major axis L1) of the primary particles was 0.7 μm. The thickness of the secondary particle outer shell (shell) was 1.2 μm, the particle porosity was 23.7%, and the positive electrode active material A had a BET specific surface area of 0. It is adjusted within the range of 0.5 to 1.9 m ² / g.

[Preparation of positive electrode sheet]
The positive electrode active material A obtained above, acetylene black (AB) as a conductive material, and polyvinylidene fluoride (PVDF) as a binder, N so that the mass ratio of these materials is 90: 8: 2. -Methyl-2-pyrrolidone (NMP) was mixed to prepare a slurry-like composition for forming a positive electrode mixture layer. This composition is uniformly applied to both sides of a long sheet-like aluminum foil (positive electrode current collector: thickness 15 μm) so that the basis weight per side is 11.2 mg / cm ² (solid content basis). By attaching, drying and compressing, a sheet-like positive electrode (positive electrode sheet) in which a positive electrode mixture layer was formed on both surfaces of the positive electrode current collector was produced. The density of the positive electrode mixture layer is adjusted within the range of 1.8 to 2.4 g / cm ³ .

[Production of negative electrode active material]
A structure in which amorphous carbon is coated on the surface of graphite particles by mixing and impregnating natural graphite powder and pitch with a mass ratio of 96: 4 and firing in an inert atmosphere at 800 to 1300 ° C. for 10 hours. Carbon particles were obtained. The carbon particles were sieved to obtain a negative electrode active material having an average particle diameter (D ₅₀ ) of 5 to 40 μm and a BET specific surface area of 3.0 to 6.0 m ² / g.

[Preparation of negative electrode sheet]
The negative electrode active material, styrene-butadiene copolymer (SBR) as a binder, and carboxymethyl cellulose (CMC) as a thickener, the mass ratio of these materials is 98.6: 0.7: 0. A slurry-like composition for forming a negative electrode mixture layer was prepared by mixing with ion-exchanged water so as to be 7. This composition was uniformly applied to both sides of a long sheet-like copper foil (thickness 10 μm) so that the basis weight per side was 7.3 mg / cm ² (solid content basis), and after drying By compressing, a sheet-like negative electrode (negative electrode sheet) in which a negative electrode mixture layer was formed on both surfaces of the negative electrode current collector was produced. The density of the negative electrode mixture layer is adjusted within the range of 0.9 to 1.3 g / cm ³ .

[Preparation of separator sheet with heat-resistant barrier layer]
As a separator sheet, a long separator sheet (thickness: 20 μm) having a three-layer structure composed of polypropylene (PP) / polyethylene (PE) / polypropylene (PP) was prepared. The thickness of each layer was 7 μm for each PP layer and 6 μm for the PE layer. A heat-resistant barrier layer was formed on one side of this separator sheet. That is, alumina (“AKP-3000” manufactured by Sumitomo Chemical Co., Ltd., average particle size 0.48 μm) as an inorganic filler, an acrylic binder as a binder, and CMC as a thickener, and a mass ratio thereof. Was mixed with ion-exchanged water so as to be 96.7: 2.6: 0.7 to prepare a slurry-like composition for forming a heat-resistant barrier layer. Mixing was performed using an ultrasonic disperser “CLEAMIX” manufactured by M Technique Co., Ltd. for 5 minutes at 15000 rpm and for 15 minutes at 20000 rpm. The obtained composition for forming a heat-resistant barrier layer was applied by a gravure coating method so as to cover the entire surface of the separator sheet, and dried at a temperature of 70 ° C. to form a heat-resistant barrier layer. In the gravure coating, the line speed of the separator sheet was 3 m / min, the gravure roll speed was 3.8 m / min, and the speed ratio (gravure speed / line speed) was 1.27. In this manner, a separator sheet with a heat-resistant barrier layer having a heat-resistant barrier layer having a thickness of 5.0 μm formed on one side was produced.

[Construction of lithium secondary battery]
The produced positive electrode sheet and negative electrode sheet are laminated and wound through the two separator sheets with a heat-resistant barrier layer, and the rolled body is pressed and ablated from the side direction to form a flat-shaped bag. A rotating electrode body was produced. The separator sheet was disposed so that the heat-resistant blocking layer was opposed to the positive electrode sheet. The electrode terminals were joined to the ends of the positive and negative electrode current collectors of the produced wound electrode body, and housed in an aluminum prismatic battery case together with the non-aqueous electrolyte, and then the battery case was sealed. As the non-aqueous electrolyte, a mixed solvent containing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 3: 3: 4, and LiPF ₆ as a supporting salt is about 1 The one contained at a concentration of mol / L was used. In addition, an electrolytic solution in which difluorophosphate (LiPO ₂ F ₂ ) and lithium bisoxalate borate (LiBOB) are arbitrarily dissolved as a single substance or a mixture at a rate of about 0.05 mol / L is used. You can also. Thus, a test lithium secondary battery having a battery capacity of 3.8 Ah was assembled. In this secondary battery, the above-described initial capacity ratio (C _N / C _P ) is adjusted to 1.5 to 1.9.

<Example 2>
A separator sheet with a heat-resistant barrier layer was prepared in the same manner as in Example 1 except that a heat-resistant barrier layer (thickness per side: 5.0 μm) was formed on both sides of the separator sheet. A secondary battery was constructed.

<Example 3>
A test lithium secondary battery according to Example 3 was constructed in the same manner as in Example 1 except that the separator sheet was disposed so that the heat-resistant blocking layer was opposed to the negative electrode sheet.

<Example 4>
[Preparation of positive electrode active material B having a solid structure]
In a reaction tank equipped with an overflow pipe and set to a temperature of 40 ° C., ion-exchanged water is placed, and nitrogen gas is circulated while stirring to pass through the reaction tank with an oxygen gas (O ₂ ) concentration of 2.0%. Adjusted to oxidizing atmosphere. Next, a 25% aqueous sodium hydroxide solution and 25% aqueous ammonia were added so that the pH measured based on the liquid temperature of 25 ° C. was 12.0 and the NH ₄ ⁺ concentration in the liquid was 15 g / L. In nickel sulfate, cobalt sulfate and manganese sulfate, the molar ratio of Ni: Co: Mn is 0.34: 0.33: 0.33, and the total molar concentration of these metal elements is 1.8 mol / L. Was dissolved in water to prepare a mixed aqueous solution. This mixed aqueous solution, 25% NaOH aqueous solution, and 25% aqueous ammonia are supplied into the reaction vessel at a constant rate so that the average residence time of the precipitated NiCoMn composite hydroxide particles is 10 hours. After controlling the pH to be 12.0 and the NH ₄ ⁺ concentration to be 15 g / L and continuously crystallizing the reaction vessel to become a steady state, NiCoMn composite hydroxide (product) from the overflow pipe Were collected continuously, washed with water and dried. Thus, a composite hydroxide having a composition represented by Ni _0.34 Co _0.33 Mn _0.33 (OH) _{2 + α} (where α is 0 ≦ α ≦ 0.5). Particles were obtained.

The composite hydroxide particles were heat-treated at 150 ° C. for 12 hours in an air atmosphere. Next, Li ₂ CO ₃ as a lithium source and the composite hydroxide particles were mixed so that the molar ratio of Li: (Ni + Co + Mn) (that is, m _Li : m _T ) was 1.14: 1. This mixture was calcined at 760 ° C. for 4 hours and then at 950 ° C. for 10 hours. Thereafter, the fired product was crushed and sieved. In this way, a positive electrode active material B having an average composition represented by Li _1.14 Ni _0.34 Co _0.33 Mn _0.33 O ₂ was obtained. This positive electrode active material B was confirmed to have a dense (solid) structure by SEM image observation. The average particle diameter of the secondary particles was 5.5 μm, the particle diameter of the primary particles was 0.9 μm, and the thickness of the secondary particle outer shell was 4.8 μm. Further, the BET specific surface area of the positive electrode active material B is adjusted within a range of 0.5 to 1.9 m ² / g.

[Construction of lithium secondary battery]
A test lithium secondary battery according to Example 4 was constructed in the same manner as Example 3 except that the positive electrode active material B prepared above was used instead of the positive electrode active material A.

[Evaluation of thermal stability]
Each lithium secondary battery constructed as described above was evaluated for thermal stability under the following conditions. That is, after performing an appropriate initial conditioning process, the battery was forcibly shut down by performing a continuous main charge test, and the magnitude of the leakage current thereafter was evaluated. Specifically, as an initial conditioning process, a constant current charge is performed at room temperature (25 ° C.) at a charge rate of 1/10 C for 3 hours, and then a constant current constant voltage up to 4.1 V at a charge rate of 1/3 C. The operation of charging at 3 and the operation of discharging at a constant current up to 3.0 V at a discharge rate of 1/3 C were repeated 2-3 times.

  As a continuous main charge test, low current discharge was performed at −10 ° C. until the state of SOC was 30%, and then constant current charge was performed from the state of SOC of 30% until the maximum voltage reached 40 V at a current of 40A. In this continuous main charging test, a current value (leakage current value) for 10 minutes after the battery was shut down was measured. The maximum current value in 10 minutes is shown in Table 1 as “leakage current value”. Here, the relationship between the current of the lithium secondary battery and the temperature in the battery in the continuous main charge test is shown in FIG. FIG. 6 shows that the temperature in the battery is lowered by suppressing the current (leakage current) after the shutdown (in the direction indicated by the arrow in the figure). From this relationship, it can be evaluated that if the leakage current value is 2 A or less, the heat generation of the battery after shutdown is suppressed and the thermal stability is excellent.

  As shown in Table 1, the secondary batteries according to Examples 1 and 2 in which a positive electrode active material having a hollow structure is used and a heat-resistant barrier layer is disposed between the positive electrode and the separator are leak currents in a thermal stability test. The value was 2A or less. On the other hand, in the secondary battery according to Example 3 in which the positive electrode active material having a hollow structure was used and the heat-resistant barrier layer was disposed between the negative electrode and the separator, the leakage current value in the thermal stability test exceeded 2A. In Example 4 using the positive electrode active material having a solid structure, the leakage current value was 2 A or less even though the heat-resistant barrier layer was disposed between the negative electrode and the separator. From these results, it can be seen that the increase in the leakage current is a phenomenon peculiar when a positive electrode active material having a hollow structure is used. In addition, in a secondary battery using a positive electrode active material having a hollow structure, by disposing a heat-resistant barrier layer between the positive electrode and the separator, heat generation of the battery after shutdown can be suppressed, and heat stability can be excellent. Recognize. This is because a heat-resistant barrier layer is arranged between the positive electrode and the separator, so that the melt of the separator is blocked by the heat-resistant barrier layer and does not enter the positive electrode, and the decrease in the shape retention of the separator is suppressed. It is thought that it was because it was done.

  Specific examples of the present invention have been described in detail above, but these are merely examples and do not limit the scope of the claims. The invention disclosed herein may include various modifications and alterations of the specific examples described above.

1 Automobile (vehicle)
DESCRIPTION OF SYMBOLS 10 Battery case 12 Opening part 14 Cover body 20 Winding electrode body 25 Non-aqueous electrolyte (non-aqueous electrolyte)
30 Positive electrode (positive electrode sheet)
32 Positive Current Collector 34 Positive Electrode Mixing Layer 35 Positive Current Collector Laminating Section 36 Positive Electrode Mixing Layer Non-Forming Section 37 Internal Positive Terminal 38 External Positive Terminal 40 Negative Electrode (Negative Sheet)
42 Negative electrode current collector 44 Negative electrode composite material layer 45 Negative electrode current collector layered portion 46 Negative electrode composite material layer non-formed portion 47 Internal negative electrode terminal 48 External negative electrode terminal 50A, 50B Separator (separator sheet)
51 Heat-resistant barrier layer 100 Lithium secondary battery 110 Positive electrode active material particles (positive electrode active material)
112 Primary particle 115 Shell portion 115a Shell inner surface 115b Shell outer surface 116 Hollow portion 118 Through hole

Claims (7)

A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode,
The positive electrode includes a positive electrode active material having a hollow structure having a shell part and a hollow part formed therein, and a heat-resistant blocking layer is disposed between the positive electrode and the separator ,
The positive electrode active material has a particle porosity of 5% or more,
The non-aqueous electrolyte secondary battery , wherein the thickness of the shell of the positive electrode active material is 3.0 μm or less .   The nonaqueous electrolyte secondary battery according to claim 1, wherein a particle porosity of the positive electrode active material is 15% or more.   The nonaqueous electrolyte secondary battery according to claim 1, wherein the thickness of the shell of the positive electrode active material is 2 μm or less.   The nonaqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein the heat-resistant barrier layer has a thickness of 2 µm or more.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the separator is made of a polyolefin-based resin.   The heat-resistant barrier layer contains a filler as a main component, and the filler is at least one selected from the group consisting of alumina, boehmite, silica, titania, zirconia, calcia, and magnesia. The non-aqueous electrolyte secondary battery described in 1.   A vehicle equipped with the nonaqueous electrolyte secondary battery according to claim 1.

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